Starting with the application of various cytokines like IL-2 or IFN α-2b, a variety of immunologic anti-cancer strategies have been developed such as the use of adoptive T cell therapy, oncolytic viruses, cancer vaccines, and the use of immune checkpoint inhibitors (ICI) as monoclonal antibodies targeting CTLA-4 and PD-1 or its ligand PD-L1 as the most important development in cancer therapy during the past decade. The gene discussed is PDCD1; the disease is cancer.